werkator/src/main/kotlin/de/hoennig/gittally/git/GitService.kt

package de.hoennig.gittally.git

import de.hoennig.gittally.config.ConfigLoader
import org.slf4j.LoggerFactory
import org.springframework.stereotype.Service
import java.nio.file.Path
import java.nio.file.Paths
import java.time.Duration
import java.time.Instant
import java.time.OffsetDateTime

@Service
class GitService(
    private val runner: GitCommandRunner,
    private val configLoader: ConfigLoader,
) {
    private val log = LoggerFactory.getLogger(GitService::class.java)

    fun getTopLevel(workingDir: Path = Paths.get(".")): Path {
        val result = runner.run(listOf("git", "rev-parse", "--show-toplevel"), workingDir)
        if (!result.isSuccess) {
            throw RuntimeException("Not a git repository")
        }
        return Paths.get(result.stdout.trim())
    }

    fun getOriginUrl(workingDir: Path = Paths.get(".")): String? {
        val result = runner.run(listOf("git", "remote", "get-url", "origin"), workingDir)
        return if (result.isSuccess) result.stdout.trim() else null
    }

    fun fetchOrigin(workingDir: Path = Paths.get(".")) {
        authenticated(workingDir) { environment ->
            runner.runOrThrow(listOf("git", "fetch", "--prune", "origin"), workingDir, environment)
        }
    }

    fun fetchBranch(
        branch: String,
        workingDir: Path = Paths.get("."),
    ) {
        authenticated(workingDir) { environment ->
            // `--` guards against refnames starting with `-` being read as git options
            runner.runOrThrow(listOf("git", "fetch", "origin", "--", branch), workingDir, environment)
        }
    }

    fun localBranches(workingDir: Path = Paths.get(".")): List<String> =
        runner
            .runOrThrow(listOf("git", "for-each-ref", "--format=%(refname:strip=2)", "refs/heads"), workingDir)
            .lines()

    fun originBranches(workingDir: Path = Paths.get(".")): List<String> =
        runner
            .runOrThrow(listOf("git", "for-each-ref", "--format=%(refname:strip=3)", "refs/remotes/origin"), workingDir)
            .lines()
            .filter { it != "HEAD" }

    /** All origin branches with their head commit, in one git call; refnames cannot contain spaces. */
    fun originBranchHeads(workingDir: Path = Paths.get(".")): Map<String, String> =
        runner
            .runOrThrow(
                listOf("git", "for-each-ref", "--format=%(refname:strip=3) %(objectname)", "refs/remotes/origin"),
                workingDir,
            ).lines()
            .map { it.substringBeforeLast(' ') to it.substringAfterLast(' ') }
            .filter { (branch, _) -> branch != "HEAD" }
            .toMap()

    /**
     * Head commits of the remote's pull-request refs (`refs/pull/<n>/head`), which Gitea
     * exposes to plain git clients — no API token needed. A branch whose head appears
     * here has a pull request open for exactly this commit.
     */
    fun pullRequestHeads(workingDir: Path = Paths.get(".")): Set<String> =
        authenticated(workingDir) { environment ->
            runner.runOrThrow(listOf("git", "ls-remote", "origin", "refs/pull/*/head"), workingDir, environment)
        }.lines()
            .map { it.substringBefore('\t') }
            .toSet()

    /**
     * A branch has new commits when its origin counterpart is ahead of the local branch,
     * or when it exists only on origin.
     */
    fun hasNewCommits(
        branch: String,
        workingDir: Path = Paths.get("."),
    ): Boolean {
        val originRef = "refs/remotes/origin/$branch"
        if (!refExists("refs/heads/$branch", workingDir)) {
            return refExists(originRef, workingDir)
        }
        val upstream =
            runner
                .runOrThrow(listOf("git", "for-each-ref", "--format=%(upstream)", "refs/heads/$branch"), workingDir)
                .stdout
                .trim()
        val compareTo =
            when {
                upstream.isNotEmpty() -> upstream
                refExists(originRef, workingDir) -> originRef
                else -> return false
            }
        if (!refExists(compareTo, workingDir)) {
            return false
        }
        val count =
            runner
                .runOrThrow(listOf("git", "rev-list", "--count", "refs/heads/$branch..$compareTo"), workingDir)
                .stdout
                .trim()
        return count.toLong() > 0
    }

    /** Origin branches without a local counterpart whose latest commit is younger than [maxAge]. */
    fun newOriginBranches(
        maxAge: Duration,
        workingDir: Path = Paths.get("."),
    ): List<String> {
        val cutoff = Instant.now().minus(maxAge)
        val local = localBranches(workingDir).toSet()
        return runner
            .runOrThrow(
                listOf(
                    "git",
                    "for-each-ref",
                    "--sort=-committerdate",
                    "--format=%(refname:strip=3) %(committerdate:unix)",
                    "refs/remotes/origin",
                ),
                workingDir,
            ).lines()
            .mapNotNull { line ->
                val branch = line.substringBeforeLast(' ')
                val epochSeconds = line.substringAfterLast(' ').toLongOrNull() ?: return@mapNotNull null
                branch to Instant.ofEpochSecond(epochSeconds)
            }.filter { (branch, committedAt) ->
                branch != "HEAD" && branch !in local && committedAt >= cutoff
            }.map { (branch, _) -> branch }
    }

    /** Switches to an existing local branch, or creates a tracking branch from origin. */
    fun checkout(
        branch: String,
        workingDir: Path = Paths.get("."),
    ) {
        if (refExists("refs/heads/$branch", workingDir)) {
            runner.runOrThrow(listOf("git", "switch", "--", branch), workingDir)
        } else {
            runner.runOrThrow(listOf("git", "switch", "--track", "-c", branch, "refs/remotes/origin/$branch"), workingDir)
        }
    }

    /**
     * Fast-forwards local branch refs to their origin counterparts and returns the
     * branches whose ref moved. Build worktrees share the primary checkout's `.git`,
     * so tools running inside a build see these refs — checks that compare a local
     * branch against its origin counterpart (hs.hsadmin.ng's `prQuickCheck` compares
     * `master` with `origin/master`) otherwise fail on every build once origin moves on.
     *
     * Strictly non-destructive: a local ref that is not an ancestor of its origin
     * counterpart (diverged, or ahead) is left alone, the ref update is a
     * compare-and-swap against the commit just read, and the branch checked out in
     * [workingDir] is advanced with `merge --ff-only`, which refuses to run over
     * conflicting uncommitted changes.
     *
     * Call this only *after* the poll cycle picked its due branches: a local ref lagging
     * behind origin is the watcher's change signal ([hasNewCommits], `newOriginBranches`),
     * so syncing beforehand would silence the branch instead of building it.
     */
    fun fastForwardLocalBranches(workingDir: Path = Paths.get(".")): List<String> {
        val originHeads = originBranchHeads(workingDir)
        val checkedOut = currentBranch(workingDir)
        return localBranches(workingDir).filter { branch ->
            val origin = originHeads[branch] ?: return@filter false
            val local = localHeadCommit(branch, workingDir) ?: return@filter false
            if (local == origin || !isAncestor(local, origin, workingDir)) {
                return@filter false
            }
            // the `refs/` prefix keeps the refname from being read as a git option
            val result =
                if (branch == checkedOut) {
                    runner.run(listOf("git", "merge", "--ff-only", "refs/remotes/origin/$branch"), workingDir)
                } else {
                    runner.run(listOf("git", "update-ref", "refs/heads/$branch", origin, local), workingDir)
                }
            if (!result.isSuccess) {
                log.warn("not fast-forwarding local branch {}: {}", branch, result.stderr.trim())
            }
            result.isSuccess
        }
    }

    /** True when [ancestor] is reachable from [descendant]; false for diverged or unrelated commits. */
    private fun isAncestor(
        ancestor: String,
        descendant: String,
        workingDir: Path,
    ): Boolean = runner.run(listOf("git", "merge-base", "--is-ancestor", ancestor, descendant), workingDir).isSuccess

    fun resetHardToOrigin(
        branch: String,
        workingDir: Path = Paths.get("."),
    ) {
        // no `--` here: with paths `git reset --hard` refuses to run; the `origin/` prefix
        // already keeps the argument from looking like an option
        runner.runOrThrow(listOf("git", "reset", "--hard", "origin/$branch"), workingDir)
    }

    fun commitTimestamp(
        sha: String,
        workingDir: Path = Paths.get("."),
    ): Instant =
        OffsetDateTime
            .parse(
                runner
                    .runOrThrow(listOf("git", "show", "-s", "--format=%cI", sha), workingDir)
                    .stdout
                    .trim(),
            ).toInstant()

    fun currentBranch(workingDir: Path = Paths.get(".")): String? =
        runner
            .runOrThrow(listOf("git", "branch", "--show-current"), workingDir)
            .stdout
            .trim()
            .ifEmpty { null }

    /** The commit `refs/heads/[branch]` points at, or null when there is no such local branch. */
    fun localHeadCommit(
        branch: String,
        workingDir: Path = Paths.get("."),
    ): String? {
        val result = runner.run(listOf("git", "rev-parse", "--verify", "refs/heads/$branch"), workingDir)
        return if (result.isSuccess) result.stdout.trim() else null
    }

    /** The commit `refs/remotes/origin/[branch]` points at, or null when the branch is not on origin. */
    fun originHeadCommit(
        branch: String,
        workingDir: Path = Paths.get("."),
    ): String? {
        val result = runner.run(listOf("git", "rev-parse", "--verify", "refs/remotes/origin/$branch"), workingDir)
        return if (result.isSuccess) result.stdout.trim() else null
    }

    fun headCommit(workingDir: Path = Paths.get(".")): String =
        runner
            .runOrThrow(listOf("git", "rev-parse", "HEAD"), workingDir)
            .stdout
            .trim()

    /** Creates a worktree at [path] with [commit] checked out as a detached HEAD; [path] must not exist yet. */
    fun worktreeAdd(
        path: Path,
        commit: String,
        workingDir: Path = Paths.get("."),
    ) {
        runner.runOrThrow(listOf("git", "worktree", "add", "--detach", path.toString(), commit), workingDir)
    }

    /** Removes registrations of worktrees whose directories no longer exist. */
    fun worktreePrune(workingDir: Path = Paths.get(".")) {
        runner.runOrThrow(listOf("git", "worktree", "prune"), workingDir)
    }

    /** Checks out [commit] as a detached HEAD, discarding local modifications to tracked files. */
    fun checkoutDetached(
        commit: String,
        workingDir: Path = Paths.get("."),
    ) {
        runner.runOrThrow(listOf("git", "checkout", "--force", "--detach", commit), workingDir)
    }

    private fun refExists(
        ref: String,
        workingDir: Path,
    ): Boolean = runner.run(listOf("git", "show-ref", "--quiet", "--verify", ref), workingDir).isSuccess

    /**
     * Runs [block] with askpass credentials from config for HTTPS origins.
     * SSH origins and missing credentials run without auth setup;
     * terminal prompts are always disabled so a fetch can never hang on stdin.
     */
    private fun <T> authenticated(
        workingDir: Path,
        block: (environment: Map<String, String>) -> T,
    ): T {
        val noPrompt = mapOf("GIT_TERMINAL_PROMPT" to "0")
        if (getOriginUrl(workingDir)?.startsWith("http") != true) {
            return block(noPrompt)
        }
        val git = configLoader.load(getTopLevel(workingDir)).git
        if (git.account.isBlank() || git.token.isBlank()) {
            return block(noPrompt)
        }
        return GitAskPass.withAskPass(git.account, git.token, block)
    }
}