const builtin = @import("builtin");
const std = @import("std");
const Build = std.Build;

pub fn addCoverageStep(b: *Build, root_module: *Build.Module) *Build.Step.Compile {
    //verify host requirements
    {
        const supported = builtin.os.tag == .linux and
            (builtin.cpu.arch == .x86_64 or builtin.cpu.arch == .aarch64);

        if (!supported)
            @panic("Coverage only supported on x86_64-linux or aarch64-linux");
    }

    // Add options
    const coverage_threshold = b.option(u8, "coverage-threshold", "Minimum coverage percentage required") orelse 0;
    const coverage_dir = b.option([]const u8, "coverage-dir", "Coverage output directory") orelse
        b.pathJoin(&.{ b.build_root.path orelse ".", "coverage" });
    const coverage_step = b.step("coverage", "Generate test coverage report");

    // Set up kcov download
    // We can't do it directly because we are sandboxed during build, but
    // we can create a program and run that program. First we need the destination
    // directory
    const kcov = blk: {
        const arch_name = switch (builtin.cpu.arch) {
            .x86_64 => "x86_64",
            .aarch64 => "aarch64",
            else => unreachable,
        };

        const Algo = std.crypto.hash.sha2.Sha256;
        var hasher = Algo.init(.{});
        hasher.update("kcov-");
        hasher.update(arch_name);
        var cache_hash: [Algo.digest_length]u8 = undefined;
        hasher.final(&cache_hash);

        const cache_dir = b.pathJoin(&.{
            b.cache_root.path.?,
            "o",
            b.fmt("{s}", .{std.fmt.bytesToHex(cache_hash, .lower)}),
        });

        const kcov_name = b.fmt("kcov-{s}", .{arch_name});
        break :blk .{ .path = b.pathJoin(&.{ cache_dir, kcov_name }), .arch = arch_name };
    };

    // Create download and coverage build steps
    return blk: {
        const download_exe = b.addExecutable(.{
            .name = "download-kcov",
            .root_module = b.createModule(.{
                .root_source_file = b.path("build/download_kcov.zig"),
                .target = b.resolveTargetQuery(.{}),
            }),
        });

        const run_download = b.addRunArtifact(download_exe);
        run_download.addArg(kcov.path);
        run_download.addArg(kcov.arch);

        const run_coverage = b.addSystemCommand(&.{kcov.path});
        run_coverage.addArgs(&.{ "--include-path", "src/" });
        const css_file = b.pathJoin(&.{ b.build_root.path.?, "build", "bcov.css" });
        run_coverage.addArg(b.fmt("--configure=css-file={s}", .{css_file}));
        run_coverage.addArg(coverage_dir);
        const test_exe = b.addTest(.{
            .root_module = root_module,
            // we need to set the test exe to use llvm as the self hosted backend
            // does not support the data kcov needs
            .use_llvm = true,
        });
        run_coverage.addArtifactArg(test_exe);
        run_coverage.step.dependOn(&test_exe.step);
        run_coverage.step.dependOn(&run_download.step);

        if (coverage_threshold > 0) {
            const xml_path = b.fmt("{s}/test/cobertura.xml", .{coverage_dir});
            const check_step = CheckCoverage.create(b, xml_path, coverage_threshold);
            check_step.step.dependOn(&run_coverage.step);
            coverage_step.dependOn(&check_step.step);
        } else {
            coverage_step.dependOn(&run_coverage.step);
        }
        break :blk test_exe;
    };
}

pub const CheckCoverage = struct {
    step: Build.Step,
    xml_path: []const u8,
    threshold: u8,

    pub fn create(owner: *Build, xml_path: []const u8, threshold: u8) *CheckCoverage {
        const check = owner.allocator.create(CheckCoverage) catch @panic("OOM");
        check.* = .{
            .step = Build.Step.init(.{
                .id = .custom,
                .name = "check coverage",
                .owner = owner,
                .makeFn = make,
            }),
            .xml_path = xml_path,
            .threshold = threshold,
        };
        return check;
    }

    fn make(step: *Build.Step, options: Build.Step.MakeOptions) !void {
        _ = options;
        const check: *CheckCoverage = @fieldParentPtr("step", step);
        const allocator = step.owner.allocator;

        const file = try std.fs.cwd().openFile(check.xml_path, .{});
        defer file.close();

        const content = try file.readToEndAlloc(allocator, 10 * 1024 * 1024);
        defer allocator.free(content);

        const needle = "line-rate=\"";
        const start = std.mem.indexOf(u8, content, needle) orelse return error.CoverageNotFound;
        const value_start = start + needle.len;
        const value_end = std.mem.indexOfScalarPos(u8, content, value_start, '"') orelse return error.CoverageNotFound;
        const value_str = content[value_start..value_end];

        const coverage = try std.fmt.parseFloat(f64, value_str);
        const coverage_int: u8 = @intFromFloat(coverage * 100.0);

        if (step.owner.verbose) {
            var stdout_buffer: [1024]u8 = undefined;
            var stdout_writer = std.fs.File.stdout().writer(&stdout_buffer);
            const stdout = &stdout_writer.interface;
            try stdout.print("Coverage: {d}%\n", .{coverage_int});
        }

        if (coverage_int < check.threshold)
            return step.fail("Coverage {d}% is below threshold {d}%", .{ coverage_int, check.threshold });
    }
};