//! The pipeline itself: `cargo ndk` -> `javac`/`d8` -> `aapt2` ->
//! `zipalign` -> `apksigner`, with no Gradle driving *this* file's steps.
//!
//! **One disclosed exception**, recorded here rather than left to be
//! rediscovered: step 3 below still runs `./gradlew
//! :shellApp:printRuntimeClasspathJars` once, because `app/shellApp`
//! depends on the `:link` submodule (Kotlin: `ServerStore`/`ServerSettings`,
//! the Keystore-sealed enrollment, RUST.md's E3 entry explains why that
//! code is reused rather than re-derived in Rust) and on
//! `androidx.core:core-ktx` (used at runtime through JNI by
//! `android-shell`'s `notify.rs`, for `NotificationCompat` and friends).
//! Both are ordinary Maven/AAR dependency graphs, and reimplementing a
//! dependency resolver to avoid one Gradle invocation was not a good trade
//! against "smallest honest route" (RUST.md's E5 box) -- especially since
//! that one call also compiles `:link`'s Kotlin as a side effect, using
//! Gradle's own embedded Kotlin compiler. This machine has no standalone
//! `kotlinc` (checked: not on PATH, not under any SDK), so that side
//! effect is what answers E3's open question about `kotlinc` -- see
//! RUST.md's E5 entry for the full account. Nothing past this one call
//! touches Gradle: `javac`, `d8`, `aapt2`, `zipalign` and `apksigner` are
//! invoked directly, and the jars this call resolves are consumed as
//! plain binary inputs to `d8`, exactly like any other pre-built `.jar`.

use std::path::{Path, PathBuf};
use std::process::Command;

use crate::keystore::{self, Signer};
use crate::sdk::{self, Sdk};
use crate::{Fail, Variant};

const APPLICATION_ID: &str = "com.example.aiapp.shell";

pub fn build(variant: Variant, abis: &[String]) -> Result<PathBuf, Fail> {
    let repo_root = repo_root()?;
    let app_dir = repo_root.join("app");
    let shell_app_dir = app_dir.join("shellApp");
    let android_shell_dir = repo_root.join("android-shell");

    let sdk = sdk::find()?;
    sdk::require_ndk_installed(&sdk.root)?;
    require_cargo_ndk()?;

    let out_dir = repo_root.join("target").join("xtask").join("apk");
    std::fs::create_dir_all(&out_dir).map_err(|e| {
        Fail::new(
            "could not create the xtask output directory",
            &e.to_string(),
            "check permissions under target/",
        )
    })?;

    println!("==> Building android-shell for {}", abis.join(", "));
    build_native_libs(&android_shell_dir, &shell_app_dir, &sdk, abis)?;

    println!("==> Resolving the runtime classpath (one Gradle call -- see apk.rs's module doc)");
    let classpath_jars = runtime_classpath_jars(&app_dir, &sdk)?;

    println!("==> Compiling the Java stub classes");
    let ca_pem = pinned_ca_pem()?;
    let classes_jar = compile_java(&out_dir, &shell_app_dir, &sdk, &ca_pem)?;

    println!("==> Dexing");
    let dex_dir = out_dir.join("dex");
    dex(&sdk, &classes_jar, &classpath_jars, &dex_dir)?;

    println!("==> Linking resources with aapt2");
    let base_apk = out_dir.join("base.apk");
    aapt2_link(&sdk, &shell_app_dir, &base_apk)?;

    println!("==> Merging dex and native libraries");
    let merged_apk = out_dir.join("merged.apk");
    merge(&base_apk, &dex_dir, &shell_app_dir, abis, &merged_apk)?;

    println!(
        "==> Aligning and signing ({})",
        match variant {
            Variant::Release => "release key",
            Variant::Debug => "debug key",
        }
    );
    let signer = match variant {
        Variant::Release => keystore::release_signer()?,
        Variant::Debug => keystore::debug_signer()?,
    };
    let variant_name = match variant {
        Variant::Release => "release",
        Variant::Debug => "debug",
    };
    let signed_apk = out_dir.join(format!("ai-app-shell-{variant_name}.apk"));
    align_and_sign(&sdk, &merged_apk, &signed_apk, &signer)?;

    // Copied into a Gradle-shaped path (`build/outputs/apk/<mode>/*.apk`
    // under this xtask's own directory) as the final step, purely so Dev
    // Updater's fixed-pattern APK discovery (`discover.rs`'s
    // `APK_PATTERNS`, which has no per-component path override) finds it
    // without needing a change on that side -- `.dev-updater.ron`'s
    // `shell` component points its `cwd` here. The working files above
    // stay under `target/xtask/apk/`, an ordinary build-cache location.
    let published_dir = repo_root.join("xtask/build/outputs/apk").join(variant_name);
    std::fs::create_dir_all(&published_dir).map_err(|e| {
        Fail::new(
            "could not create the published APK directory",
            &e.to_string(),
            "check permissions under xtask/build",
        )
    })?;
    let published_apk = published_dir.join(format!("ai-app-shell-{variant_name}.apk"));
    std::fs::copy(&signed_apk, &published_apk).map_err(|e| {
        Fail::new(
            "could not publish the signed APK",
            &e.to_string(),
            "check permissions under xtask/build",
        )
    })?;

    Ok(published_apk)
}

fn repo_root() -> Result<PathBuf, Fail> {
    // xtask's own Cargo.toml is at <repo_root>/xtask/Cargo.toml.
    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
    manifest_dir.parent().map(Path::to_path_buf).ok_or_else(|| {
        Fail::new(
            "could not find the repo root",
            "CARGO_MANIFEST_DIR has no parent",
            "run through cargo, not by hand",
        )
    })
}

fn require_cargo_ndk() -> Result<(), Fail> {
    run_checked(
        Command::new("cargo").args(["ndk", "--version"]),
        "cargo-ndk is not installed",
        "cargo install cargo-ndk",
    )
    .map(|_| ())
}

/// `cargo ndk`'s `-t` target name for each ABI, and `-P 26` -- the API
/// level every other cross-compile in this repo uses (RUST.md: E0, E1, E3,
/// I2), kept consistent here rather than picked fresh.
fn build_native_libs(
    crate_dir: &Path,
    shell_app_dir: &Path,
    sdk: &Sdk,
    abis: &[String],
) -> Result<(), Fail> {
    let jni_libs = shell_app_dir.join("src/main/jniLibs");
    let mut cmd = Command::new("cargo");
    cmd.current_dir(crate_dir);
    cmd.arg("ndk");
    for abi in abis {
        cmd.args(["-t", abi]);
    }
    cmd.args(["-P", "26", "-o"]).arg(&jni_libs);
    // Always the release profile for the native library, independent of
    // the APK's signing variant -- a debug build's Vulkan object-labelling
    // segfaults this emulator's driver (RUST.md's E1 entry), and there is
    // no reason for this crate's debug build to be bigger or slower for a
    // signing choice that has nothing to do with it.
    cmd.args(["build", "--release", "-p", "android-shell"]);
    cmd.env("ANDROID_HOME", &sdk.root);
    cmd.env("ANDROID_SDK_ROOT", &sdk.root);
    run_checked(
        &mut cmd,
        "cargo ndk build failed",
        "see the compiler output above",
    )
    .map(|_| ())
}

fn runtime_classpath_jars(app_dir: &Path, sdk: &Sdk) -> Result<Vec<PathBuf>, Fail> {
    let mut cmd = Command::new(app_dir.join("gradlew"));
    cmd.current_dir(app_dir);
    cmd.args(["--console=plain", ":shellApp:printRuntimeClasspathJars"]);
    cmd.env("ANDROID_HOME", &sdk.root);
    cmd.env("ANDROID_SDK_ROOT", &sdk.root);
    run_checked(
        &mut cmd,
        "resolving app/shellApp's dependencies with Gradle failed",
        "see the Gradle output above",
    )?;

    let list_file = app_dir.join("shellApp/build/xtask/runtime-classpath.txt");
    let contents = std::fs::read_to_string(&list_file).map_err(|e| {
        Fail::new(
            "printRuntimeClasspathJars did not produce its output file",
            &format!("{}: {e}", list_file.display()),
            "check app/shellApp/build.gradle.kts's printRuntimeClasspathJars task",
        )
    })?;
    Ok(contents
        .lines()
        .filter(|l| !l.is_empty())
        .map(PathBuf::from)
        .collect())
}

/// The CA this build pins, found the same way `build-apk.sh` and
/// `androidApp`/`shellApp`'s Gradle `generatePinnedCa` tasks do:
/// `$AI_APP_CA`, else `$XDG_CONFIG_HOME/ai-app/certs/ca.pem`.
fn pinned_ca_pem() -> Result<String, Fail> {
    let path = std::env::var_os("AI_APP_CA")
        .map(PathBuf::from)
        .unwrap_or_else(|| {
            let config_home = std::env::var_os("XDG_CONFIG_HOME")
                .map(PathBuf::from)
                .unwrap_or_else(|| {
                    PathBuf::from(std::env::var_os("HOME").unwrap()).join(".config")
                });
            config_home.join("ai-app").join("certs").join("ca.pem")
        });
    let pem = std::fs::read_to_string(&path).map_err(|e| {
        Fail::new(
            &format!("no CA certificate at {}", path.display()),
            &e.to_string(),
            "start ai-server (or app/ui-sandbox.sh) once on this machine first -- it generates the CA this build pins",
        )
    })?;
    let pem = pem.trim().to_string();
    if !pem.starts_with("-----BEGIN CERTIFICATE-----") {
        return Err(Fail::new(
            &format!("{} is not a PEM certificate", path.display()),
            "missing the BEGIN CERTIFICATE header",
            "point AI_APP_CA at a valid one",
        ));
    }
    Ok(pem)
}

fn compile_java(
    out_dir: &Path,
    shell_app_dir: &Path,
    sdk: &Sdk,
    ca_pem: &str,
) -> Result<PathBuf, Fail> {
    let gen_dir = out_dir.join("generated-java");
    let package_dir = gen_dir.join("com/example/aiapp/shell");
    std::fs::create_dir_all(&package_dir).map_err(|e| {
        Fail::new(
            "could not create the generated-sources directory",
            &e.to_string(),
            "check permissions under target/",
        )
    })?;
    // Same shape as shellApp's Gradle `generatePinnedCa` task: the text
    // block must start immediately after the opening `"""`, or
    // CertificateFactory stops recognising the "-----BEGIN" preamble (a
    // real bug this project hit once -- see AGENTS.md's "Things that have
    // bitten").
    let pinned_ca_java = format!(
        "package com.example.aiapp.shell;\n\npublic final class PinnedCa {{\n    private PinnedCa() {{}}\n    public static final String PINNED_CA_PEM = \"\"\"\n{ca_pem}\"\"\";\n}}\n"
    );
    std::fs::write(package_dir.join("PinnedCa.java"), pinned_ca_java).map_err(|e| {
        Fail::new(
            "could not write PinnedCa.java",
            &e.to_string(),
            "check permissions under target/",
        )
    })?;

    let classes_dir = out_dir.join("classes");
    std::fs::create_dir_all(&classes_dir).map_err(|e| {
        Fail::new(
            "could not create the classes directory",
            &e.to_string(),
            "check permissions under target/",
        )
    })?;

    let java_dir = shell_app_dir.join("src/main/java/com/example/aiapp/shell");
    let mut cmd = Command::new("javac");
    cmd.args(["-cp"]).arg(&sdk.android_jar);
    cmd.args(["-d"]).arg(&classes_dir);
    cmd.arg(java_dir.join("MainActivity.java"));
    cmd.arg(java_dir.join("NotificationService.java"));
    cmd.arg(package_dir.join("PinnedCa.java"));
    run_checked(&mut cmd, "javac failed", "see the compiler output above")?;

    let classes_jar = out_dir.join("classes.jar");
    let mut cmd = Command::new("jar");
    cmd.current_dir(&classes_dir);
    cmd.args(["cf"])
        .arg(&classes_jar)
        .args(["-C", "."])
        .arg(".");
    run_checked(
        &mut cmd,
        "jar failed to package the compiled classes",
        "see the output above",
    )?;
    Ok(classes_jar)
}

fn dex(
    sdk: &Sdk,
    classes_jar: &Path,
    classpath_jars: &[PathBuf],
    dex_dir: &Path,
) -> Result<(), Fail> {
    std::fs::create_dir_all(dex_dir).map_err(|e| {
        Fail::new(
            "could not create the dex output directory",
            &e.to_string(),
            "check permissions under target/",
        )
    })?;
    let mut cmd = Command::new(sdk.tool("d8"));
    cmd.args(["--release", "--min-api"])
        .arg(sdk::MIN_SDK.to_string());
    cmd.arg("--lib").arg(&sdk.android_jar);
    cmd.arg("--output").arg(dex_dir);
    cmd.arg(classes_jar);
    cmd.args(classpath_jars);
    run_checked(&mut cmd, "d8 failed", "see the compiler output above").map(|_| ())
}

fn aapt2_link(sdk: &Sdk, shell_app_dir: &Path, base_apk: &Path) -> Result<(), Fail> {
    let manifest_src = shell_app_dir.join("src/main/AndroidManifest.xml");
    let manifest_text = std::fs::read_to_string(&manifest_src).map_err(|e| {
        Fail::new(
            "could not read the manifest",
            &format!("{}: {e}", manifest_src.display()),
            "check app/shellApp/src/main/AndroidManifest.xml",
        )
    })?;
    // The checked-in manifest has no `package` attribute -- Gradle injects
    // it from `android.namespace` during its own manifest merge, which
    // this pipeline does not run. aapt2 needs it to know what package to
    // generate resources under.
    if manifest_text.contains("package=") {
        return Err(Fail::new(
            "app/shellApp's manifest already has a package attribute",
            "aapt2_link() assumes it doesn't and injects one",
            "update aapt2_link() in xtask/src/apk.rs to stop injecting a second one",
        ));
    }
    let merged_manifest = manifest_text.replacen(
        "<manifest ",
        &format!("<manifest package=\"{APPLICATION_ID}\" "),
        1,
    );
    let merged_manifest_path = base_apk.with_file_name("AndroidManifest.merged.xml");
    std::fs::write(&merged_manifest_path, merged_manifest).map_err(|e| {
        Fail::new(
            "could not write the merged manifest",
            &e.to_string(),
            "check permissions under target/",
        )
    })?;

    let mut cmd = Command::new(sdk.tool("aapt2"));
    cmd.args(["link", "-o"]).arg(base_apk);
    cmd.args(["--manifest"]).arg(&merged_manifest_path);
    cmd.arg("-I").arg(&sdk.android_jar);
    cmd.args(["--min-sdk-version", &sdk::MIN_SDK.to_string()]);
    cmd.args(["--target-sdk-version", &sdk::COMPILE_SDK.to_string()]);
    cmd.args(["--version-code", "1", "--version-name", "1.0"]);
    run_checked(&mut cmd, "aapt2 link failed", "see the output above").map(|_| ())
}

fn merge(
    base_apk: &Path,
    dex_dir: &Path,
    shell_app_dir: &Path,
    abis: &[String],
    merged_apk: &Path,
) -> Result<(), Fail> {
    std::fs::copy(base_apk, merged_apk).map_err(|e| {
        Fail::new(
            "could not copy the base APK",
            &e.to_string(),
            "check permissions under target/",
        )
    })?;

    let mut cmd = Command::new("jar");
    cmd.current_dir(dex_dir);
    cmd.args(["uf"])
        .arg(std::path::absolute(merged_apk).unwrap_or_else(|_| merged_apk.to_path_buf()));
    cmd.args(["classes.dex"]);
    run_checked(
        &mut cmd,
        "jar failed to add classes.dex to the APK",
        "see the output above",
    )?;

    // Android's zip layout wants "lib/<abi>/*.so" at the archive root, but
    // cargo ndk's `-o` wrote "jniLibs/<abi>/*.so" (matching the Gradle
    // source-set layout it was pointed at) -- so this stages a "lib/"
    // directory rather than trying to rename inside the zip.
    let stage = merged_apk.with_file_name("lib-stage");
    if stage.exists() {
        std::fs::remove_dir_all(&stage).ok();
    }
    for abi in abis {
        let so_name = "libandroid_shell.so";
        let src = shell_app_dir
            .join("src/main/jniLibs")
            .join(abi)
            .join(so_name);
        if !src.is_file() {
            return Err(Fail::new(
                &format!("no native library built for {abi}"),
                &format!("expected {}", src.display()),
                "check cargo ndk's output above for that ABI",
            ));
        }
        let dest_dir = stage.join("lib").join(abi);
        std::fs::create_dir_all(&dest_dir).map_err(|e| {
            Fail::new(
                "could not stage the native library",
                &e.to_string(),
                "check permissions under target/",
            )
        })?;
        std::fs::copy(&src, dest_dir.join(so_name)).map_err(|e| {
            Fail::new(
                "could not stage the native library",
                &e.to_string(),
                "check permissions under target/",
            )
        })?;
    }
    let mut cmd = Command::new("jar");
    cmd.current_dir(&stage);
    cmd.args(["uf"])
        .arg(std::path::absolute(merged_apk).unwrap_or_else(|_| merged_apk.to_path_buf()));
    cmd.arg("lib");
    run_checked(
        &mut cmd,
        "jar failed to add the native libraries to the APK",
        "see the output above",
    )
    .map(|_| ())
}

fn align_and_sign(
    sdk: &Sdk,
    merged_apk: &Path,
    final_apk: &Path,
    signer: &Signer,
) -> Result<(), Fail> {
    let aligned_apk = merged_apk.with_file_name("aligned.apk");
    let mut cmd = Command::new(sdk.tool("zipalign"));
    cmd.args(["-f", "-p", "4"])
        .arg(merged_apk)
        .arg(&aligned_apk);
    run_checked(&mut cmd, "zipalign failed", "see the output above")?;

    let mut cmd = Command::new(sdk.tool("apksigner"));
    cmd.args(["sign", "--ks"]).arg(&signer.keystore);
    cmd.arg("--ks-pass")
        .arg(format!("pass:{}", signer.password));
    cmd.arg("--ks-key-alias").arg(&signer.alias);
    cmd.arg("--out").arg(final_apk);
    cmd.arg(&aligned_apk);
    run_checked(
        &mut cmd,
        "apksigner failed to sign the APK",
        "see the output above",
    )
    .map(|_| ())
}

fn run_checked(cmd: &mut Command, what: &str, fix: &str) -> Result<(), Fail> {
    let status = cmd.status().map_err(|e| {
        Fail::new(
            what,
            &format!("could not run {:?}: {e}", cmd.get_program()),
            fix,
        )
    })?;
    if status.success() {
        Ok(())
    } else {
        Err(Fail::new(
            what,
            &format!("{:?} exited with {status}", cmd.get_program()),
            fix,
        ))
    }
}