IMPORTANT: see the github page for details of all changes made. Small fixes won't be mentioned elsewhere.

https://github.com/Kondikka/expertai

If you are looking for EAI for older HOI versions, download it from the github site. You'll find them under tags.

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Expert AI 5.0

Overhauled AI research
* New priority research AI system that works in parallel with the regular research AI.
* Making the AI research techs in very specific orders and under various conditions is very hard with the regular research AI in the game. This system solves that by having the AI select techs from a priority research queue that overrides any other ideas the AI has.
* In practice, it means I can implement more optimal research strategies for the AI, such as:
** At the start of the game, pick up these specific techs in this exact order to optimize industry build-up.
** If it's 1940 and you are still not researching fighter tech 2 and you care about building fighters, I don't care what you are doing, just pick up that damn tech and all the design requirements as your next techs.
** The AI needs to make a design that requires X Y and Z techs? Bit of a nightmare to script that into the old system but now I can just put the required research path into a script and give it a high priority.
** The AI unlocked a national focus that gives research bonuses that should be used immediately to rush certain techs while avoiding techs that would waste that research bonus? Easy-ish now, nearly impossible before.

I've added more general priority research strategies for basically all research paths in the game. They make sure that if there is a tech that the AI actually needs (it's just a generally important tech or the AI needs it for a specific design or template it wants to make), it will want to prioritize that tech.
Along with these, there are more specific strategies, such as:
* UK rushes fighter or heavy fighter research after unlocking Fighter Command.
* USA prioritizes getting good strategic bomber designs earlier.
* Germany prioritizes getting good submarine designs earlier.
* Germany rushes 3 construction techs at the start using the national focus bonus AND does not waste the bonuses on other industrial techs .
* Germany/USSR properly rushes tank techs for whatever armor type it wants if USSR accepts the tech treaty AND they don’t waste the bonuses on armor/engine techs.

Overhauled priority construction AI
For anyone interested in the details, in this mod there are 3 types of construction AI:
* The regular HOI AI that manages and queues regular buildings. This is not great for this mod because there is not a ton of moddable control over why the AI wants certain buildings and where it places them in the queue.
* The EAI building AI system that suppresses the HOI building AI logic and determines from the mod side how many of each type of shared slot building the AI wants to queue.
* The EAI priority construction system which is a separate building queue that works along with the regular game queue. This works by diverting civilian factories the AI normally uses for constructions into "Special Projects". Priority constructions function the same as regular constructions when it comes to modifiers, costs, speeds and such. They are used by the mod to create strategies for the AI to build in highly specific ways that are otherwise impossible to script dynamically or otherwise. They make the AI build specific buildings in specific states and provinces, with a queue managed and manipulated by the mod AI alone. This is what enables creating an industrial strategy for AI USSR that more closely matches the meta strategies players come up with, or having the AI in general build radar, air bases, anti-air, forts with the appropriate urgency depending on the situation.

Changes from the old priority construction system:
* The old version was a copy-paste of a system from another mod of mine, so it was just barely enough to get the job done. The new system allows the AI an unlimited amount of queued projects for example, and doesn’t work by using timed decisions.
* It recalculates daily the building speed of every project, accounting for changes in modifiers, infrastructure etc., so it should mechanically match the regular constructions in the game aside from benefiting from the new market bonus.
* It has the ability to clear the regular construction queue for the AI, as well as force the AI not to queue any shared slot buildings in order to have complete control over construction. This is for cases where every factory has to be carefully managed and the construction queue juggled for efficiency.
* Support for provincial type buildings, assigning a priority to certain projects, sorting the priority construction queue in various ways, other stuff.
* Whichever type of construction logic the AI uses depends on the situation and country. The AI is not railroaded to do a certain thing every game, the scripts are designed to be dynamic and to adapt to changes. Only the USSR currently has a more minmax type construction strategy for example, but the scripting is still dynamic to some extent. If the USSR is left alone till '41, it's going to try to maximize its industry for late game. If it gets into a bigger war before then, it will abandon the strategy and so on.

Reworked air base construction
* The AI uses the priority construction system to build air bases with a much more expanded logic for determining locations. It will account for things such as distance (closer to enemy but not too close), try to match the enemy's ability to deploy planes around each border state, avoids building one giant airbase but prefers upgrading existing ones, and so on. It generally looks for locations to help its frontlines as well as naval control by building on isolated states (islands, larger multi-state islands, enclaves like Gibraltar etc.).

Reworked anti-air construction
* To counter heavy strategic bombing, the AI tracks the frequency of bombing activity and damage levels per region. If it considers them too high, the AI will start priority constructing state anti-air around those regions.

Fort building
* Added a number of fort priority construction strategies for majors.
** Extensive strategies for USSR, reactively creating fortification lines in backline areas where the enemies are pushing near. It will build a ton of forts, but should minimize impact on industrial expansion as it only fortifies as needed.
** Also added many fortification strategies for majors for reactively fortifying islands, cities, creating fort lines when being invaded, when enemies pushing near etc.
* A generic strategy for AI to fortify victory points near enemies when it determines it is losing a war, with more importance on the capital state, as well as creating perimeter fortifications around its capital state city provinces, with increasing amounts of factories allocated to priority constructions depending on how fast the enemy progresses through its territory.
* If it looks like the war is stagnant or its frontlines aren’t changing too fast, the AI starts fortifying its front lines in places where the front doesn't move too much.
* There should be a ton more forts than you usually see from the AI, but I don’t want it to build massive forts on every border in a way that is *too* immersion breaking. So, it’s somewhere in-between the AI never building useful forts at all and AI abusing forts. It would be interesting to hear good feedback on this.

Overhauled naval designs, production and research
* Old bugs fixed that may have prevented the AI from building newer designs.
* Complete rework of all designs the AI wants to make. More effective, less ridiculously expensive designs.
* Destroyer production: it will try to maintain screening efficiency for its number of capital ships by switching screen production to a very cheap destroyer design as needed.
* The AI avoids doing a lot of incremental ship design upgrades and instead creates complete designs once it has all the requirements for it. For some ship designs there are a couple intermediary upgrade steps (for example, adding a radar module once it is researched). For various reasons, this is the best way to handle it in this mod.

Divisions and land equipment designs
* Complete rework of armor templates and equipment designs.
* Most notable armor template/design changes:
** No SP-AA or SP-ART types in these divisions.
** 50/50 ratio of motorized/armor brigades
** Added flame tank support (basic hull, fuel drums etc.), light tank recon (not sure this is useful) to all designs.
* Medium/heavy/modern tank destroyers brigades used in every division.
* Before the AI unlocks full size divisions, it will make 26w type templates even if it wants 40w templates.
* AI will upgrade to mechanized infantry and modern armor versions of the medium/heavy armor templates it has.
* The new design restrictions (template size, support columns) have made it harder to get the AI to create complex templates. I had to create more complicated scripted systems to guide the AI’s armor template upgrades because I wanted to 100% guarantee that the AI creates complex late-game designs.
* The mod’s AI military focus types for armor designs no longer change templates the AI makes and instead changes how it designs its tanks, mostly armor levels but in some cases module changes.
* The light, heavy armor templates and designs generally mirror the medium armor types, so they are probably far less optimal. I don’t have a good, detailed source for effective light, heavy armor templates/designs.
* AI can now research, design and build amphibious divisions that replace its marine divisions.
** For countries with a large industry and interest in building marine divisions (so usually USA in the late game, perhaps Japan, UK).
** Uses a template based on the regular armor division template it uses, with infantry substituted with amtrac and armor substituted with amphibious armor of the same type.
** Amphibious tank designs are similar to the regular tank designs it wants to build but with an amphibious drive.