// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! See LICENSE for licensing information.
//!
//! This build.rs script provides Cargo _features_ indicating the target ICU4C library version,
//! enabling some conditionally compiled Rust code in this crate that depends on the particular
//! ICU4C version.
//!
//! Please refer to README.md for instructions on how to build the library for your use.

#[cfg(feature = "icu_config")]
mod inner {
    use {
        anyhow::{Context, Result},
        std::process,
    };

    /// A `Command` that also knows its name.
    struct Command {
        name: String,
        rep: process::Command,
    }

    impl Command {
        /// Creates a new command to run, with the executable `name`.
        pub fn new(name: &'static str) -> Self {
            let rep = process::Command::new(&name);
            let name = String::from(name);
            Command { name, rep }
        }

        /// Runs this command with `args` as arguments.
        pub fn run(&mut self, args: &[&str]) -> Result<String> {
            self.rep.args(args);
            let stdout = self.stdout()?;
            Ok(String::from(&stdout).trim().to_string())
        }

        // Captures the stdout of the command.
        fn stdout(&mut self) -> Result<String> {
            let output = self
                .rep
                .output()
                .with_context(|| format!("could not execute command: {}", self.name))?;
            let result = String::from_utf8(output.stdout)
                .with_context(|| "could not convert output to UTF8")?;
            Ok(result.trim().to_string())
        }
    }

    /// A command representing an auto-configuration detector.  Use `ICUConfig::new()` to create.
    pub struct ICUConfig {
        rep: Command,
    }

    impl ICUConfig {
        /// Creates a new ICUConfig.
        pub fn new() -> Self {
            ICUConfig {
                rep: Command::new("pkg-config"),
            }
        }
        /// Obtains the major-minor version number for the library. Returns a string like `64.2`.
        pub fn version(&mut self) -> Result<String> {
            self.rep
                .run(&["--modversion", "icu-i18n"])
                .with_context(|| "while getting ICU version; is pkg-config in $PATH?")
        }

        /// Returns the config major number.  For example, will return "64" for
        /// version "64.2"
        pub fn version_major() -> Result<String> {
            let version = ICUConfig::new().version()?;
            let components = version.split('.');
            let last = components
                .take(1)
                .last()
                .with_context(|| format!("could not parse version number: {}", version))?;
            Ok(last.to_string())
        }

        pub fn version_major_int() -> Result<i32> {
            let version_str = ICUConfig::version_major()?;
            Ok(version_str.parse().unwrap())
        }
    }
}

#[cfg(feature = "icu_config")]
fn main() -> anyhow::Result<()> {
    std::env::set_var("RUST_BACKTRACE", "full");
    let icu_major_version = inner::ICUConfig::version_major_int()?;
    println!("icu-major-version: {}", icu_major_version);
    if icu_major_version >= 64 {
        println!("cargo:rustc-cfg=feature=\"icu_version_64_plus\"");
    }
    if icu_major_version >= 67 {
        println!("cargo:rustc-cfg=feature=\"icu_version_67_plus\"");
    }
    if icu_major_version >= 68 {
        println!("cargo:rustc-cfg=feature=\"icu_version_68_plus\"");
    }
    // Starting from version 69, the feature flags depending on the version
    // number work for up to a certain version, so that they can be retired
    // over time.
    if icu_major_version <= 69 {
        println!("cargo:rustc-cfg=feature=\"icu_version_69_max\"");
    }
    println!("done");
    Ok(())
}

/// No-op if icu_config is disabled.
#[cfg(not(feature = "icu_config"))]
fn main() {}